According to known methods a winding package consisting of contacting or separated and spaced apart windings is formed on a storage body. The insertion system pulls the yarn from the winding package over the front end of the storage body. The windings on the storage body may be advanced forward by different advance assemblies. The storage body is axially longer than the winding package. During withdrawal a yarn balloon is formed which generates significant yarn tension variations and a considerable yarn tension which both delay the insertion. In order to achieve high insertion speeds a considerable energy input thus is needed in the insertion system. On the other hand this means a high mechanical load for the weft yarn. The most important drawback is the long insertion time dictated by this method, i.e. the time period between the start of the insertion and the arrival of the then stopped weft yarn at the opposite fabric edge. The basically very high efficiency potential of modem weaving machines cannot be used satisfactorily due to the long insertion time of such known insertion methods. Furthermore, other methods are known according to which the insertion system does not directly withdraw the weft yarn from the winding package on a storage body but instead weft yarn material is presented for the insertion system in loose and substantially tensionless condition. The influence of a yarn balloon is avoided thereby such that higher insertion speeds can be achieved with low energy input while the weft yarn material is treated with respect. For example, a weft yarn portion is presented by mechanical means in zigzag form or loop form. The mechanical means release the weft yarn portion in synchronism with the withdrawal motion. The method needs high efforts in terms of the devices but is too slow for modem weaving machines because of the mass inertia of the mechanical elements and a plurality of very precisely controlled movements of the mechanical elements.
There are further methods according to which the weft yarn is presented by mechanical means in a single large loop to the insertion system. The loop is released with the start of the insertion. In this case an undesirably large space is needed and the achievable insertion speeds are limited.
Finally, it is known to present the weft yarn section to the insertion system loosely and substantially without tension in random configuration in the interior of a cavity. The random configuration of the weft yarn section easily might lead to disturbances due to weft yarn breakages and yarn tension variations during the withdrawal.
It is an object of the invention to provide a method and a yarn feeding device, as mentioned above, which allow to achieve optimal short insertion times with low energy consumption and high operational safety in highly efficient modem weaving machines.
Said object is achieved by the features of the yarn feeding device and method as disclosed herein.
Surprisingly, the winding package portion set free from the support for the withdrawal in orderly arranged windings shows a tendency, among others, due to the inherent inertia property and the form stability of the windings, to safely remain in a tubular configuration in the free space even without any mechanical inner suspension and such that the weft yarn during withdrawal first runs inwardly from the tube without forming any balloon and then runs further centrally and consumes the windings from the tube in a clean fashion, even up to the last in-fed winding which may still be supported on the support. The released winding package section does not collide. The windings do not tend to entangle or to collapse, provided that the withdrawal is carried out rapidly and in a timewise precisely controlled adaptation to the release of the winding package section. Astonishingly short insertion times can be achieved by the method. The astonishingly short insertion times allow to optimally use the capabilities of modern weaving machines in terms of high yarn speeds and high insertion frequencies. The released yarn package section may be supported from the outer side. Such a suspension, however, is more a safety measure. Expediently, the winding on speed of the substantially continuous winding process may be matched with the insertion frequency and the length of the respective inserted weft yarn section such that each insertion substantially consumes the released winding package section before a subsequent winding package section is released. Even in case of extremely high yarn speeds it can be seen that the centrally withdrawn weft yarn does consume the first winding in withdrawal direction substantially radially inwardly and without any ballooning and that the tubular configuration of the windings in the released winding package section is maintained till the end of the insertion with optimum yarn geometry. The released winding package section may contain a number of yarn windings which substantially correspond to the weft yarn length which is to be inserted, or may contain a larger number corresponding to several weft yarns which are to be inserted one after the other.
It may be expedient to overlap the withdrawal timewise with the release of the winding package section such that the released winding package section or the windings at the withdrawal side of the winding package section, respectively, have as little time as possible to leave the tubular configuration of the orderly arranged windings.
The method can be carried out in a simple way if the windings in the winding package section are set free by axial overfilling of the inner support beyond the withdrawal side end of the support. The released windings are consumed during the withdrawal before the released winding package section can collide or get into a state of disorder. The overfilling is carried out by continuous winding on of new weft yarn material.
Alternatively or additively the windings may be released by advancing the winding package on the support beyond the withdrawal side end of the support. In this case advance assemblies of any suitable kind may be employed.
In order to maintain the tubular configuration of the released yarn package section as stably as possible, and in order to optionally even use the natural adhesion between the contacting windings, the winding package and the released winding package section may be conveyed in withdrawal direction obliquely upwards.
A further alternative may be to release the windings in the winding package section released for withdrawal by a respective conveying movement or adjusting movement of at least a part of the support. In this case mechanical adjusting devices of the support may be employed.
It is important for the course of the method to extend the tendency of the released winding package section to remain freely in space without inner mechanical suspension as long as possible. This tendency also depends on the form stability of the yarn material and the windings and from the at least preliminarily inherent form stability of the winding package section. The form stability is good when the windings are wound on the support with a curvature of the yarn material which at least substantially corresponds to the smallest natural and unforced capability of the weft yarn material to store a curvature. Said capability to store the curvature may be explained as follows: a section of the weft yarn material is laid on a smooth surface. Both ends of the section are brought towards each other as close as possible. By this the weft yarn section receives a certain curvature. If then both ends are released, the weft yarn section will relax into a residual curvature representing the smallest natural capability to store a curvature. Surprisingly, it has been found that different weft yarn materials behave only slightly differently or behave even very similarly. In case that the weft yarn material in the winding package is wound at least substantially with the smallest natural capability to store a curvature, then the windings in the released winding package section will not have a considerable tendency to increase or decrease the winding radius themselves such that the released winding package section maintains the tubular configuration formed by the winding process on the inner support relatively long even if there is no further support from inside. Any adhesion between the equally formed contacting windings can support this effect.
In case of insertion methods employing an insertion system which itself cannot precisely measure the length of the respective inserted weft yarn section it may be expedient to mechanically measure the weft yarn section between the insertion system and the winding package section remaining on the support. For that purpose mechanical systems may be employed which are controlled in adaptation to the weaving cycles.
The yarn feeding device is designed predominantly but not restrictive for the measurement of the weft yarn length for a weaving machine which is unable to measure the weft yarn length by itself, e.g. a jet weaving machine. In order to hardly influence the formation of the yarn winding package and the release of the yarn winding package section by the measurement or the definition of the correct weft yarn length for each insertion, the engaging stop element is moved into the stop position without using a separate drive, but by the forward moving yarn winding package only. The stop element is brought into the engagement position just in front of a winding just generated on the support and in a position suitable for measuring the length without interfering with the conveying movement of the winding package. Then the stop element drifts with the forwardly conveyed winding package until finally the stop position is reached where the stop element defines the end of the withdrawn weft yarn length. In order to bring the stop element later again into the home position, a power drive is provided which moves the stop element exclusively in the moved away release position and substantially opposite to the withdrawal direction while at the same time yarn windings can be withdrawn without hindrance by the moved away stop element. This results in a stepwise method run during which the power drive always returns the stop element while the yarn package moves the stop element forward. In the engaging stop position the stop element is responsible for the termination of the insertion.
Expediently, the stop element functionally co-operates with a yarn clamp which is responsible for the start of the insertion and which is controlled in timewise adaptation to the operation movements of the stop element. The yarn clamp holds the weft yarn firmly while the disengaged stop element is returned to the home position. The yarn clamp releases the weft yarn first precisely at the start of the insertion cycle. The insertion then is terminated when the engaging stop element has reached the stop position and is caught at the stop position, before the yarn clamp again holds the yarn in preparation for the return motion of the stop element.
When the stop element terminates the insertion in the engaging stop position, the weft yarn may be subjected to a significant longitudinal tension between the stop element and the insertion system or between the stop element and even the weaving machine. The longitudinal tension acts backwards at least towards the stop element. The weft yarn section between the yarn clamp adjusted into the clamping position and holding the yarn and the stop element as well will remain under longitudinal tension. In case that then the stop element would be moved from the engaging stop position into no longer engaging the release position, the tension depending friction of the weft yarn at the moving stop element could disturb the tubular configuration of the yarn winding package. Furthermore, the unavoidably occurring relaxation of the tensioned yarn during the movement of the stop element into the release position also could cause a disorder of the tubular configuration of the yarn windings. However, by means of the auxiliary drive the yarn clamp holding the yarn can be adjusted such that by an adjustment travel of the yarn clamp in the direction towards the stop element still positioned in the engaging stop position the weft yarn section extending therebetween becomes gradually relaxed and will be totally relaxed as soon as the stop element then moves into the release position for the next insertion. This adjustment of the yarn clamp avoids damages to the tubular configuration of the yarn winding package. Basically, it also may be expedient, to move the yarn clamp out of the moving space of the yarn at least in the final phase of an insertion, e.g. with the help of a further actuator or even with the same auxiliary drive. This minimises the danger that the yarn might be caught by the yarn clamp. Under certain conditions it might suffice to move a shield for a short while over the clamping region of the yarn clamp, or to provide a deflector at the yarn clamp or adjacent to the clamping region of the yarn clamp which deflector then guides the yarn sidewardly past the clamping region, namely at the sides from which the yarn normally enters the clamping region.
In order to move as little mass as possible during the movement of the stop element in withdrawal direction by the yarn winding package, a hinge should be provided between the stop element and the power drive of the stop element. Furthermore, the stop element ought to be guided in its moving direction in order to have precise positioning at least in the stopping position which is important for measuring the yarn length. The guidance either may be achieved by a defined hinge axis perpendicular to the withdrawal direction and/or a guiding curve in the support or even in a structure adjacent to the support at the outer side, which guiding curve then may extend exactly in this direction.
A power drive on a magnetic basis is constructionally simple and functionally safe. A stationary solenoid pulls or pushes the at least partially magnetically conductive stop element in the released position back into the home position by using the hinge. Alternatively, for the same purpose other drives might be employed instead.
A correct positioning of the stop element in the stop position may be achieved by a stop provided in the guiding notch either in the support or in the outwardly located adjacent structure. The yarn winding package moves the stop element in conveying direction against the stop.
Since by an abrupt stop of the withdrawn weft yarn in the stop position of the stop element unavoidably a whiplash effect or sudden stretching occurs in connection with a momentary yarn tension rise in this technique, conventionally a controlled yarn brake (end-of-insertion-brake) is employed which dampens the tension rise. Such controlled yarn brakes are expensive and need a complicated control system. For this reason and according to the invention in a structurally simple way the yarn instead is dampened at the stop position of the stop element precisely at the location where the whiplash effect or the stretching effect occurs, namely at the stop element; The dampening is carried out by deflecting the stop element counter to a predetermined elastic counter force essentially in circumferential direction of the support and by the energy which is transferred on the stop element by the stop the weft yarn. By deflecting the stop element counter to the elastic counter force the weft yarn is decelerated gradually and energy will be dissipated to significantly alleviate or remove the weft yarn tension peak. For this reason a controlled yarn brake can be omitted here.
The above-mentioned function e.g. can be achieved by using a stop element which itself is designed for an elastic return behaviour, e.g. with a springy hinge portion such that the stop element is deflected like a bending spring only under the energy increase of the whiplash effect to alleviate the yarn tension rise. Alternatively a sidewardly positioned retainer could be provided for the stop element in the support or in the structure adjacent to the support. The retainer then is temporarily dislocated sidewardly under the force of the weft yarn counter to the predetermined counter force and together with the sidewardly moving stop element in order to dissipate energy. As soon as the whiplash effect is over the retainer or stop element, respectively, is returned in circumferential direction into the predetermined correct length defining stop position.
The yarn clamp which is responsible for the start of the insertion has considerable importance since the point in time of the release of the weft yarn has to be adapted very precisely to the operation of the weaving machine and since only a very short time should expire between the command to start the insertion and the actual release of the weft yarn. For that reason the yarn clamp is used as the trigger of the insertion. The yarn clamp should occupy as little space in the yarn path and should act just as close in front of the front end of the support that the released yarn package section can be set free for the insertion with the desired size and without any mechanical interference. The adjustability of the yarn clamp in withdrawal direction, either in a linear or a pivoting motion, is important in order to relax the weft yarn section provided between the yarn clamp holding the yarn and the stop element positioned in the stop position after the insertion, and, under certain conditions, to move a yarn disturbing part of the yarn clamp at least substantially out of the yarn moving area. A step motor is e.g. a useful rotational drive. A solenoid assembly can be used as a linear drive.
An effective clamping at a small spot and with precisely adjusted clamping force may be achieved by a notch-like clamping region in a slim protrusion of the yarn clamp. The clamping force is mechanically generated by spring force. This can be done, because the clamping action for the yarn is of timewise secondary importance since then the weft yarn is caught by the stop element anyway. The spring force has to assure that the clamping force is sufficient for safely holding the weft yarn back even under tension produced by the insertion system.
Of importance is, however, that the yarn clamp releases the weft yarn precisely at the desired point in time and as rapidly as possible, when an insertion is to be introduced. This can be achieved by a switching solenoid in a functionally simple way. The armature of the switching solenoid is in an initial position with an intermediate predetermined distance from a bolt tightly holding the weft yarn while the switching solenoid is excited. Thanks to the intermediate distance the armature has sufficient time to overcome the static starting friction and to convert the increasing magnetic force in high speed and to build up high kinetic energy and to accelerate strongly before the armature hits the bolt. The switching solenoid then does not need to overcome the spring force by accelerating the armature from speed zero, but overcomes the counter force of the spring abruptly by the then accelerated and by the high kinetic energy of the armature. This results in an abrupt release of the clamped weft yarn. In practice, release times in a range of only one millisecond can be achieved.
While the yarn winding package has the tendency to keep the tubular configuration for a longer time in its released section which is no longer suspended from the inner side, it may be expedient, to then support the yarn winding package from the outer side at least in certain regions on guiding surfaces. The suspension from the outer side maintains the tubular configuration and allows during withdrawal to withdraw the weft yarn from the first winding radially inwardly and then along the prolongation of the axis of the support such that no balloon is formed which could cause a delay and could dissipate energy, and such that the desired high insertion speeds or the short insertion times, respectively, are achieved.
The guiding surfaces could be formed such that they suspend at least the lower half of the released yarn winding package section. In some cases even a bigger part or even the entire yarn winding package section may be suspended. In this case the guiding surfaces could be formed by surface parts or rods or the like in order to generate as low friction as possible on the released yarn winding package section, or to generate friction only there where it might be expedient, e.g. at an upper location at the front most windings in withdrawal direction in order to prevent that those windings may inadvertently tilt forwardly.
Alternatively or additively at least a part of the guiding surface may be inclined upwardly in withdrawal direction. This contributes to maintain the released yarn winding package section compact and dense while it moves forwards, and even during withdrawal of the yarn.
A further alternative may be to move the guiding surface together with the forwardly conveyed yarn winding package in order to keep friction influences between the guiding surface and the yarn winding package as low as possible. This may be achieved, e.g. by a caterpillar structure of driven guiding surfaces which hold and convey the yarn winding package from the outer side like spaced apart gear wheels. At the end of an insertion even the last yarn winding on the support may be consumed up to the stop element in the stop position. The undesirable whiplash effect or stretching effect could then lead to an undesirable increase of the weft yarn tension. For that reason a hold-back element with the shape of a lamella or a brush could be provided on top of the yarn winding package. The element co-operates with the front end of the support to slow down the weft yarn speed before the weft yarn comes to a total standstill at the stop element. This element has to be adjustable such that it comes into action only at the respective desired point in time, namely at the end of the insertion, but does not influence the released yarn winding package section during the remaining time period.
In a structurally simple way the support is designed as a rod cage. The fingers of the rod cage may have individual eccentric adjustment devices with a common adjusting eccentric which is accessible from the front side of the support. In this way diameter variations of the rod cage can be made comfortably. Since the support for carrying out the method has a relatively small diameter, approximately corresponding to the smallest natural and unforced capability of the weft yarn material to store a curvature, a simple eccentric adjustment device is enough, because a diameter variation corresponding to the length of one yarn winding only requires a relatively small radial adjustment stroke.
Here two possibilities can be realised. The adjusting eccentric either is rotated in the carrier and displaces the finger outwardly or inwardly, or the adjusting eccentric is rotated in the finger and is displaced within the carrier together with the finger and via the eccentric portion.
An outer diameter between about 20 mm and about 50 mm is expedient for the support, preferably between about 30 mm to about 40 mm. This is a diameter range corresponding to the smallest natural and unforced capability to store a curvature of most of the weft yarn materials processed nowadays.
Since, of course, any disturbance of the tubular configuration of the yarn winding package is to be avoided in order to achieve a yarn winding package as homogenous and stable as possible, and also a stable, homogenous released yarn winding package section, it may be expedient to provide the stop element at the lower side of the support where the gravitation force contributes towards avoiding disturbing influences of the stop element.
The yarn clamp should substantially be aligned in the direction of the stretched out yarn with the region at which the stop penetrates into the support.
According to a very important aspect of the invention the operational safety of the method can be improved significantly by a loop-suppressing body centrally provided at the support and projecting substantially in alignment with the support axis in withdrawal direction such that its free end is positioned at a location with a distance in front of the support. The basic advantages of the method are extremely high insertion speeds or short insertion times, respectively. This positive effect results from the fact that the yarn during withdrawal out of the frontmost winding of the released winding package section directly runs substantially radially inwardly and first then in axial direction into the weaving machine, and without any balloon formation. This yarn movement is carried out with very high speed and a high dynamic. Since the windings in the released winding package section are not supported from the inner side but remain so to speak freely in the space, particularly in case of lively yarn quality occasionally snarls may be formed which would lead to fabric faults if inserted while twisted or which then could cause disturbances in the insertion system, respectively. The snarl suppressing body supports the yarn run there where the yarn runs substantially radially inwards from the frontmost winding and then further in axial direction. In this region the suppressing body hinders by its structural presence that a snarl may get twisted. Instead the untwisted snarl will be pulled open again. The contact occurring during the running dynamic of the yarn with the suppressing body significantly also calms the yarn which then moves relatively linearly in axial direction into the insertion system.
Expediently, the snarl suppressing body has a coat surface which is rotationally symmetrical and which is tapered towards the free end. This assures that a formed snarl will slide off there and hinders that the snarls gets twisted. The shape also hinders that the snarl even might tend to wrap and tighten around the body under the withdrawal tension.
Structurally simple the snarl suppressing body is a pin, preferably a conical pin. The pin offers an ideal possibility for placing a withdrawal sensor there for registering each withdrawn winding.
The outer diameter of the pin should, at least close to its free end, only amount to a fraction of the diameter of the support.
The free end should markedly project beyond the front side of the support in order to function also in the region in which the yarn is running inwardly from the released winding package section. Preferably, the free end even is located in withdrawal direction downstream of the position of the yarn clamp in order to reach into an area downstream where snarls are no longer formed and where no danger exists that a snarl could get twisted and could form a knot.
The coat surface should be smooth and should have a low coefficient of friction, optionally the coat surface should have a low friction overlay. Low friction has the meaning that the surface should generate only low friction with the yarn material. This is because the suppressing body only by its bodily presence and extension substantially in withdrawal direction has to effect that snarls which are in process of being generated cannot be twisted. The body should impose as little mechanical and delaying load as possible on the yarn.
Expediently the forward advancing movement of the winding package is initiated by means of a predetermined conicity of the support. The cone-conveying principle leads to the advantage of directly contacting yarn windings which then also may stick to each other in the released yarn winding package section. Furthermore, this is a low cost and safe solution.
Alternatively an advancing principle employing a wobbling element in the support may be used which is driven in synchronism with the winding the element, does not rotate but generates a wobbling motion due to its inclined axis which wobbling motion is transferred onto the first yarn winding exiting from the winding element and being formed on the support. The first yarn winding then pushes further the downstream yarn windings.
As a further alternative the yarn winding package can be advanced axially with so-called yarn separation generated by driven advancing elements. The advancing elements are placed between the fingers or rods of the rod cage and use e.g. a common drive hub which has a skew axis in relation to the axis of the support or the drive axis of the winding element, respectively.
Basically, the yarn winding package section when presented for withdrawal without tension and loosely, is released by overfilling the support. As an alternative, the support may be pulled back in relation to the yarn winding package and opposite to the withdrawal direction in order to release the yarn winding package section at the right moment. In this case an assisting strip member may contribute to release the yarn winding package from the pulled back support in compact form and in tubular configuration.
According to a further alternative an auxiliary support is associated to the front side of the support. The auxiliary support is used to first form a yarn winding package supported from the inner side. Thereafter, the auxiliary support is coaxially pulled away from the support in order to release the yarn winding package section which is intended to be inserted. In this case the pull-back of the auxiliary support can be assisted by a stripper member which may be of advantage to keep the released yarn winding package section in compact shape.
The stretching effect or whiplash effect at the end of an insertion into a jet weaving machine fed by weft yarns originating from a measuring feeding device is a mechanical consequence of the abrupt deceleration of the inserted weft yarn at the stop element. In order to avoid damages, in practice controlled yarn brakes are employed which start to brake in advance before the weft yarn is caught at the stop element and which gradually decelerate the weft yarn. Controlled yarn brakes of this kind need a precise electronic control system and are complicated and costly. According to an important aspect of the invention the stop element itself which is responsible for the whiplash effect or the stretching effect when reaching the stop position, is used for dampening or attenuating the yarn tension rise at the end of an insertion. That is, the attenuation is carried out in the weft yarn exactly at the location where the undesirable yarn tension rise would come from. For that purpose the stop element can be deflected counter to a predetermined elastic force and over a dampening stroke substantially in circumferential direction of the support. In more detail, the stop element is adjusted from a first catching position in which it starts to decelerate the weft yarn over the dampening stroke into a second catching position and is loaded by the reaction force from the weft yarn, such that energy is dissipated before the weft yarn is totally stopped. The stop element then is returned by the predetermined elastic force. In toto this allows a very good yarn control resulting without yarn breakage in a finally linearly stretched weft yarn.
For this case it may be expedient to provide at least one hinge region between the linear drive which controls the stop element between the engaged position and the released position, and the support. The hinge region allows the sideward movability or this degree of freedom of the stop element without the necessity to accordingly move the linear drive as well. The damping element movably arranged with a predetermined moving direction in a stationary guide can yield against spring force. The damping element is moved by the stop element by the reaction force of the weft yarn counter to the spring force and over the dampening stroke, such that energy is dissipated and that the yarn is braked gradually without suffering from a significant yarn tension rise. The damping element does not need to move strictly in circumferential direction of the support, but could instead move obliquely in a direction approximately corresponding with the orientation of the resulting yarn reaction force at the stop element. The orientation results from the substantially circumferential force of the yarn extending between the last winding at the withdrawal side and the stop element and the substantial axial force of the downstream yarn portion. The automatic return of the damping element after the compensation of the yarn tension peak offers the advantage to then also pull back the weft yarn at least for a small distance.
In an alternative embodiment the yarn winding package already is formed with several yarn windings which are larger than adjacent ones and which define engagement locations for a respective one out of a plurality of stop elements. The stop elements may be formed like hooks and can e.g. be turned and move together with the yarn winding package such that they sequentially may engage in the enlarged windings. This particularly expedient when the yarn winding package is formed with a size which represents a weft yarn length for several subsequent insertions.